1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and more particularly, to an electrophotographic photosensitive member having functionally specialized photosensitive layers comprising a charge generation layer forming an electric charge on exposure to light and a charge transport layer transporting the generated charge.
2. Description of the Prior Art
Inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide and the like have been widely known heretofore.
On the other hand, various organic photoconductive polymers have been proposed such as polyvinyl carbazole and the like. Such polymers have indeed satisfactory transparency, film-forming property and flexibility. Nevertheless, those polymers have not been commercialized until now because they are inferior to inorganic photoconductive materials in photosensitivity, durability, and stability to the variation of the environment. A photosensitive member prepared from an organic photoconductive material of low molecular weight combined with a binder has also been proposed, but it does not have sufficient photosensitivity yet.
In order to remove such drawbacks, a laminated structure has been proposed lately wherein the photosensitive layer is functionally divided into two layers of a charge generating layer and a charge transport layer, for example, in the disclosure in the U.S. Pat. No. 3,837,851 and No. 3,871,882. The sensitivity of the photosensitive layer having such laminated structure is known to be affected by the thickness ratio of the charge generation layer to the charge transport layer, as is disclosed in Australian Laid-open Patent Specification No. 87757/75.
The inventors, after a lot of study, have found that the size distribution of the pigment used in the charge generation layer has a great influence on the photosensitivity, and have accomplished the present invention.